void main() {
  People p = People(); // 不写new也可以
  p.age = 30;
  p.name = "张三";
  p.say();
}

/*****
 * 
 * export class People {
  username: string = ""
  constrcutor (name: string) {
    this.username = name
  }
  say () {}
  run () {}
}
 * ****/

// 声明一个类
class People {
  String? name;
  int? age;

  say() {
    print('我是$name,今年$age');
  }
}
